3 Phase Question

mgriff543

Member
I recently bought a Rockwell/Delta 40C radial arm saw that is 220v 3-phase. I wired a static phase converter and it has a magnetic switch. It starts and runs good until I release the start button. I bought it off auction so I have no past history on the machine. I've got no experience with 3ph or magnetic switches so any thoughts would be appreciated.
 
Perhaps for some reason, possibly a tripped overload, or incorrect wiring, the contactor isn't latching in the "ON" position, or there's a safety switch not connected or functional?

Got any diagrams of how it's wired or documentation on the converter?

Is the contractor that won't latch a part of the convertor or part of the lathe?

If no help here there's a terrific Forum over at "Practical Machinist".
VFD and phase converters
 
Somebody who knows more will tell you more, but magnetic starters can usually be wired to either use an off/on switch (I think that is how yours is now) or where the on button energizes a coil which holds itself in and the off switch breaks the circuit for that coil.
 
Impossible to say without a schematic and preliminary troubleshooting, but my first suspect is a thermal overload (aka heater) is open.

John T
 
Are you sure the saw was working before you bought it? It sounds more like a problem with the switch than your phase converter.

The switch uses one leg to operate an electro magnet to keep the switch on. The switch should stay on until the power is interrupted by a power failure or the off switch. Until you push the off button power should be going through it too so I would check there with a volt meter. It may be one of the contacts are burned.
 

This has the typical start/stop station wiring diagrams. Sounds like the interlock contact is not making contact or it is improperly wired.

Look on page 6. The interlock contact is called "M aux". When it closes, it holds the starter in until the stop circuit is opened or power is lost. It's a safety feature to prevent the saw from starting when power is restored.
start/stop station
 
Something I didn't see mentioned is that the control voltage is on machines is often run through a transformer that drops it to 120V. That being the case, it will only work right it it's pulling power from the two regular legs. In other words, it it's pulling from one regular leg, and the manufactured leg for the second, it's no going to provide the required voltage to keep the contactor pulled in after the on button is released.

That said, I actually helped a guy repair the start/stop switch on a table saw after he'd had a couple of electricians look at it. In that case, it wouldn't start at all. I don't know how they missed the problem, but the contacts in the start button itself were bad. Changed it out, and all was good.
 
(quoted from post at 21:52:42 07/04/16)
This has the typical start/stop station wiring diagrams. Sounds like the interlock contact is not making contact or it is improperly wired.

Look on page 6. The interlock contact is called "M aux". When it closes, it holds the starter in until the stop circuit is opened or power is lost. It's a safety feature to prevent the saw from starting when power is restored.
start/stop station

I agree with Steve.
There are 4 contacts in the starter, 3 when closed send power to the motor when closed the 4th is smaller and are called holding contacts. It sounds like they are the problem, they may only need cleaning.
If you can't find the problem, I'm north east of Charlotte. I can take a look at it.


Dusty
 
40 years ago I helped my dad build his last static converter before he died. It had 2 contactors. The start contactor was controlled by an adjustable timer. It connected the start caps for about one second before dropping out. The second contactor picked up when the first one did applying power to motor and run caps. The stop button dropped it out. During the first second both the start and run caps were in the circuit.

Asking how to repair an electrical device such as a phaser is like expecting a Dr to diagnose you over the phone. Good luck find someone who knows anything about the old school static or dynamic phase converts. They all tell you to go with VFD. geo.
 
Nobody has made a comment on static converters. When I was needing a phase converter everyone said don't go there. They said for woodworking equipment there would be a great deal of power loss with a static converter. I ended up getting a rotary phase converter before hearing about a VFD which would have been better for my needs. The rotary phase converter had to be turned on and off for the occasional use I was doing. It's more suited for someone running three phase power frequently so the thing could just be left running all day.
 

Use a VFD. Soft start, true three phase power, variable speed and torque limiting incase of a jam. Saves electrical costs too.
 
I was quite surprised when I went on eBay and realized the cost of the VFDs is very reasonable. Sure is a good way to solve this.
 
Thanks for the thoughts guys. I work the next few nights so it will be a bit before I get back at it. Mike
 
Stephen, Did I miss something in the original post?

I recently bought a Rockwell/Delta 40C radial arm saw that is 220v 3-phase. I wired a static phase converter and it has a magnetic switch.

As for efficiency or The power factor, the old converts I was a part of helping my dad, I think, and remember this was 40 years ago, the best we could hope for was about 70%. Meaning you would be lucky to get 7 hp out of a 10 hp motor, ball park.

I have no idea if a VFD is more efficient of making 3 phase out of 220v and is there a reduction in HP?

Would you post a link to show efficiency or power factor?

How many people on YT have ever make converters the old school way? Many farmers back in the day before VFDs, needed 3 phase and didn't want the spend a pant load and a monthly minimum charge for it. I'm thinking it was very expensive.

Geo
 
Well, I'm not an electrician nor have built a phase converter. My main trade is a cabinetmaker which I have four old three phase machines running off a rotary phase converter. I did install the phase converter and wire the machinery but I don't have statistics on which converter is best. Buickanddeere and John T are the electricians. I had just wondered why nobody kicked on the static converter when every other place converters were discussed the static converter is on the bottom of the list due to the power loss. In a later post Buickanddeere said get a VFD because it gave you true three phase power. The rotary unit I have has 120V on L1 and L2 and uses capacitors to bump L3 to 220V to compensate for some of the power loss. What I didn't like about the rotary unit is I might run a machine for an hour or so once a week and because the rotary has a motor in the unit itself I have to turn the thing on and off as I use the machine. I think when I get the time I'm going to wire a remote control clicker to the converter.
 
Several years back I built my own rotary converter from a brand new 10HP 3 phase motor I got off CL for about $200. For the rest of it I used two contactors, and a handful of capacitors out several well pump starters.

What I did with mine was to build one that requires start capacitors. Instead of spinning it up like some do, when the start button is pushed, it causes the main contactor to pull in and hold, while an aux contactor temporarily ties the start capacitors in to spin the motor up to speed, until the button is released. It takes about a one second hold for things to work, but it beats the heck out of having to run another motor, or a pull rope on the converter motor.

Currently I've got a 5HP lathe, and a mill with both a 5HP vertical head, and a 5HP horizontal head. I have to start either the lathe, or the vertical motor on the mill to have enough to kick off the horizontal motor (due to the gearing), but once it's running I can cut off the other idler and it works just fine from there.

First opportunity I've got a factory made rotary converter that will handle starting a 10HP, and a max load of 20 HP that I want to get wired in. The rotary converter allows me to run multiple motors (ie air compressor, mill or lathe, etc) at the same time, where a VFD, like a static converter, will only run one motor at a time.

Rotaries aren't that hard to build on your own, and with a little looking they can be made relatively cheap.
 
My dad used contactor instead of push button for start cap. Turn it on and everything was automatic. Timer held start contactor in for about one second. Some phasers were for 30 HP pumps. Push button isn't big enough.
 
Stephen,

My dad had an old cast iron craftsman table saw. He put a large 3 phase motor on it and a static converter. Only took a few seconds for the motor to come up to speed. Once it did there was no stopping it. Static converters only use power when in use. Where rotors may be better at making 3 phase. If rotor gets hot, that would indicate they were using power. I don't think rotors got that warm. My dad used to take the rotor motor apart and shave metal off the rotor. He thought they worked better that way.

Keep in mind 40 years ago static and dynamic were the only thing on the market. Less efficient, yet electric company wanted to charge farmers thousands to run them 3 phase and large minimum monthly bills even if they didn't use power monthly. So as for cost savings, it was a bargain for using static converters on each motor, about 70%.

Actually the caps were used to create a phase shift in the current. 3 phase is 120 degrees. L1 and L2 on 220 is 180 degrees apart.

I don't know anything about the VFD's discussed here. I have heard where they are used on actual 3 phase motors and 3 phase power to control the speed of blower motors. Been out of working on AC's for years.

I have no 3 phase equipment. But I've has sitting on my garage floor a 5 hp 3 phase motor and all the parts I need to build converters. Been there for 30 years. As long as I have the parts, I'll most likely never need to build one.

geo
 
(quoted from post at 07:46:10 07/06/16) Stephen,

My dad had an old cast iron craftsman table saw. He put a large 3 phase motor on it and a static converter. Only took a few seconds for the motor to come up to speed. Once it did there was no stopping it. Static converters only use power when in use. Where rotors may be better at making 3 phase. If rotor gets hot, that would indicate they were using power. I don't think rotors got that warm. My dad used to take the rotor motor apart and shave metal off the rotor. He thought they worked better that way.

Keep in mind 40 years ago static and dynamic were the only thing on the market. Less efficient, yet electric company wanted to charge farmers thousands to run them 3 phase and large minimum monthly bills even if they didn't use power monthly. So as for cost savings, it was a bargain for using static converters on each motor, about 70%.

Actually the caps were used to create a phase shift in the current. 3 phase is 120 degrees. L1 and L2 on 220 is 180 degrees apart.

I don't know anything about the VFD's discussed here. I have heard where they are used on actual 3 phase motors and 3 phase power to control the speed of blower motors. Been out of working on AC's for years.

I have no 3 phase equipment. But I've has sitting on my garage floor a 5 hp 3 phase motor and all the parts I need to build converters. Been there for 30 years. As long as I have the parts, I'll most likely never need to build one.

geo

Most people seen satisfied if they can get it to "work". Doesn't matter to them a couple of windings are running hot , laminations buzzing , reduced shaft HP and reduced energy efficiency . They are terrified of anything new and would rather fool around with tech what thier grandfathers had to make do with when there was nothing better on the market.
 
So what is the powerfactor when using a VFD? I know absolutely nothing about them except they are a variable frequency device. Perhaps some day I read up on them, but for now no need for one. geo
 
(quoted from post at 15:50:34 07/06/16) So what is the powerfactor when using a VFD? I know absolutely nothing about them except they are a variable frequency device. Perhaps some day I read up on them, but for now no need for one. geo

depends on the load
 

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